In view of the rapidity of chemical reactions, the need to carry out reactions using very small amounts of a sample, on-site analysis, and so on, integration technology for carrying out chemical reactions in very small spaces has attracted attention from hitherto, and research has been carried out with vigor throughout the world.
So-called microchemical systems are one example of such integration technology. Microchemical systems are systems for carrying out mixing, reaction, separation, extraction, detection or the like on a liquid-borne sample in a very fine channel formed in a small glass substrate or the like. Examples of reactions carried out in such a microchemical system include diazotization reactions, nitration reactions, and antigen-antibody reactions. Moreover, examples of extraction/separation include solvent extraction, electrophoretic separation, and column separation. A microchemical system may be used with a single function, for example for only separation, or may be used with a combination of a plurality of functions.
As an example of a microchemical system for only separation out of the above functions, an electrophoresis apparatus for analyzing extremely small amounts of proteins, nucleic acids or the like has been proposed (see, for example, Japanese Laid-Open Patent Publication (Kokai) No. H08-178897). This electrophoresis apparatus has a channel-formed plate-shaped member comprised of two glass substrates joined together. Because the member is plate-shaped, breakage is less likely to occur than in the case of a glass capillary tube having a circular or rectangular cross section, and hence handling is easier.
In these microchemical systems, because the amount of the liquid-borne sample is very small, a highly sensitive detection method is essential. As such a method, a photothermal conversion spectroscopic analysis method that uses a thermal lens effect arising upon a liquid-borne sample in a very fine channel absorbing light has been established. This photothermal conversion spectroscopic analysis method uses a photothermal conversion effect in which light is convergently irradiated onto a liquid-borne sample, whereupon the liquid-borne sample absorbs the light and hence thermal energy is released, and thus the temperature of the solvent is locally raised by this thermal energy, whereby the refractive index thereof changes, and hence a thermal lens is formed. This photothermal conversion spectroscopic analysis method has opened up a path for realizing microchemical systems.
FIG. 5 is a view useful in explaining the principle of a thermal lens.
In FIG. 5, exciting light is convergently irradiated onto an extremely small amount of a liquid-borne sample via an objective lens of a microscope, whereby a photothermal conversion effect is brought about. For most substances, the refractive index drops as the temperature rises, and hence in the liquid containing the liquid-borne sample onto which the exciting light has been convergently irradiated, the refractive index drops, with the drop being larger the closer to the center of the converged light, which is where the rise in temperature is largest. In other words, the refractive index relatively increases with distance from the center of the converged light. This is because the rise in temperature becomes smaller with distance from the center of the converged light due to thermal diffusion. Optically, the resulting refractive index distribution produces the same effect as a concave lens, and hence the effect is referred to as the thermal lens effect. The size of the thermal lens effect, i.e. the power of the concave lens, is proportional to the optical absorbance of the liquid-borne sample. Moreover, in the case that the refractive index increases with temperature, the change in the refractive index is reversed, and hence a thermal lens effect that produces the same effect as a convex lens arises.
In the photothermal conversion spectroscopic analysis method described above, changes in the refractive index of the liquid (sample solution) containing the liquid-borne sample due to thermal diffusion in the liquid are thus observed, and hence the method is suitable for detecting the concentrations of extremely small samples in a liquid.
In the conventional photothermal conversion spectroscopic analysis apparatus, a channel-formed plate-shaped member is disposed below the objective lens of a microscope, and exciting light of a predetermined wavelength outputted from an exciting light source is introduced into the microscope. The exciting light is thus convergently irradiated via the objective lens of the microscope onto a liquid-borne sample in the channel of the channel-formed plate-shaped member. The focal position of the convergently irradiated exciting light is made to be in the sample solution, and hence a thermal lens is formed centered on this focal position.
On the other hand, detecting light having a wavelength different to that of the exciting light is outputted from a detecting light source, and is introduced into the microscope. The detecting light passes through and exits from the microscope, and is thus convergently irradiated onto the thermal lens that has been formed in the sample solution by the exciting light, and passes through the sample solution and is thus diverged or converged. The diverged or converged detecting light exiting from the sample solution forms signal light. The signal light passes through a converging lens and a filter, or just a filter, and is then detected by a detector. The intensity of the detected signal light depends on the thermal lens formed in the sample solution. Note also that alternatively the detecting light may have the same wavelength as the exciting light, or the exciting light may also be used as the detecting light.
In the photothermal conversion spectroscopic analysis apparatus described above, a thermal lens is thus formed in the focal position of the exciting light, and changes in the refractive index of the thermal lens formed are detected using detecting light that has either the same wavelength as the exciting light or a different wavelength thereto (see e.g. Japanese Laid-Open Patent Publication (Kokai) No. H10-232210).
However, with such a photothermal conversion spectroscopic analysis apparatus, the optical systems and so on for the light sources, the measurement section and the detection section (photoelectric conversion section) are complicated in system configuration, and hence such an apparatus has been large in size, and has thus lacked portability. Consequently, there is a problem that there are limitations with regard to the installation site and the operation of the photothermal conversion spectroscopic analysis apparatus.
Moreover, in the photothermal conversion spectroscopic analysis apparatus, the exciting light and the detecting light are led to the liquid-borne sample through open space, and hence various optical system components such as the light sources, mirrors and lenses must be prevented from moving during measurement, and thus a sturdy surface plate for fixing these components is required. Furthermore, the optical axes of the exciting light and the detecting light may shift out of alignment upon changes in the environment such as changes in the temperature, and hence jigs for adjusting for such shifts are required. These jigs are also a cause of the photothermal conversion spectroscopic analysis apparatus becoming larger in size and hence lacking portability.
Moreover, in a microchemical system that uses the photothermal conversion spectroscopic analysis method, in many cases it is necessary for the focal position of the exciting light and the focal position of the detecting light to be different from one another.
FIGS. 6A and 6B are views useful in explaining the formation position of a thermal lens and the focal position of detecting light in the direction of travel of exciting light; FIG. 6A shows a case in which an objective lens has chromatic aberration, and FIG. 6B shows a case in which the objective lens does not have chromatic aberration.
In the case that the objective lens 500 has chromatic aberration, as shown in FIG. 6A, the thermal lens 501 is formed at the focal position 502 of the exciting light, and the focal position 503 of the detecting light is in a position shifted by an amount ΔL from the focal position 502 of the exciting light, so that the detecting light enables changes in the refractive index of the thermal lens 501 to be detected as changes in the focal distance of the detecting light. On the other hand, in the case that the objective lens 500 does not have chromatic aberration, as shown in FIG. 6B, the focal position 503 of the detecting light is almost exactly the same as the position of the thermal lens 501 formed at the focal position 502 of the exciting light. As a result, the detecting light is not deflected by the thermal lens 501, and hence changes in the refractive index of the thermal lens 501 cannot be detected.
However, the objective lens of a microscope is generally manufactured so as not to have chromatic aberration, and hence for the reason described above, the focal position 503 of the detecting light is almost exactly the same as the position of the thermal lens 501 formed at the focal position of the exciting light (FIG. 6B). Changes in the refractive index of the thermal lens 501 thus cannot be detected. There is thus a problem that the position of the liquid-borne sample in which the thermal lens 501 is formed must be shifted from the focal position 503 of the detecting light every time measurement is carried out as shown in FIG. 7A or 7B, or else the detecting light must be diverged or converged slightly using a lens (not shown) before being introduced into the objective lens 500 so that the focal position 503 of the detecting light is shifted from the thermal lens 501 as shown in FIG. 8; consequently, the working efficiency of the user is poor.
It is an object of the present invention to provide a microchemical system which dispenses with the optical axis alignment and positioning of the focal point of the detecting light and that of the exciting light, and is capable of carrying out measurement with high sensitivity.